It is frequently necessary to store moisture sensitive materials for relatively long periods in containers. In a particular example, certain pharmaceutical substances are supplied and/or stored in small vials containing one or more unit doses of the dry substance, and having a puncturable seal through which a hypodermic needle may be inserted. By means of such a needle water may be injected into the vial, the substance dissolved in situ, and the solution then withdrawn via the needle into a syringe for short-term use before hydrolysis of the moisture sensitive material. Such puncturable seals enable this operation to be sterile. During storage the presence of atmospheric moisture within the container, or the ingress of atmospheric moisture, can cause decomposition of such materials
Often moisture sensitive pharmaceutical substances are provided in containers together with an internal desiccant in the container, for example a small sachet of molecular sieve or silica gel. Clearly this is not practical when the substance has to be made up in situ within the container as described above, as contamination by desiccant on dissolution of the substance is likely.
An example of a moisture sensitive pharmaceutical substance is clavulanic acid and its salts, such as potassium clavulanate. Potassium clavulanate is both hygroscopic and readily hydrolysed by water, so for handling and long term storage of potassium clavulanate it is necessary for the immediate environment to be kept extremely dry, e.g. 30% Relative Humidity ("RH") or less.
Potassium clavulanate is a .beta.-lactamase inhibitor, and is often provided in a formulation in combination with a partner .beta. lactam antibiotic. A partner which is often used in such formulations is amoxycillin. For injectable formulations, which may be dry reconstitutable powders or oily suspensions for i.m. injection amoxycillin is used in the form of sodium amoxycillin. In some forms sodium amoxycillin is a powerful desiccant, and when contained together with potassium clavulanate in a sealed vial such forms of sodium amoxycillin can exert a dehydrating effect which helps to preserve the potassium clavulanate. Other forms of sodium amoxycillin, such as the anhydrous crystalline form disclosed in EP 0131147 B are less desiccating, and although it would be desirable to use such forms in formulations together with potassium clavulanate, the problem arises that these forms can be insufficiently desicatting to protect the potassium clavulanate.